net: use case-insensitive host string comparison in TestLookup*

Some nameservers alter the case of records as they return, e.g
.google.COM or .Google.com.
However according to RFC4343, DNS name should be treated in case insensitive fashion.
This CL will fix case sensitive testcases.

Fixes #34781

Change-Id: I5f9f6a41ddc1c61993e8d1f934ef0febddc3adc1
Reviewed-on: https://go-review.googlesource.com/c/go/+/200277Reviewed-by: Andrei Tudor Călin <mail@acln.ro>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/lookup_test.go

@@ -21,6 +21,10 @@ import (
 	"time"
 )
 
+func hasSuffixFold(s, suffix string) bool {
+	return strings.HasSuffix(strings.ToLower(s), strings.ToLower(suffix))
+}
+
 func lookupLocalhost(ctx context.Context, fn func(context.Context, string, string) ([]IPAddr, error), network, host string) ([]IPAddr, error) {
 	switch host {
 	case "localhost":
@@ -97,11 +101,11 @@ func TestLookupGoogleSRV(t *testing.T) {
 		if len(srvs) == 0 {
 			t.Error("got no record")
 		}
-		if !strings.HasSuffix(cname, tt.cname) {
+		if !hasSuffixFold(cname, tt.cname) {
 			t.Errorf("got %s; want %s", cname, tt.cname)
 		}
 		for _, srv := range srvs {
-			if !strings.HasSuffix(srv.Target, tt.target) {
+			if !hasSuffixFold(srv.Target, tt.target) {
 				t.Errorf("got %v; want a record containing %s", srv, tt.target)
 			}
 		}
@@ -147,7 +151,7 @@ func TestLookupGmailMX(t *testing.T) {
 			t.Error("got no record")
 		}
 		for _, mx := range mxs {
-			if !strings.HasSuffix(mx.Host, tt.host) {
+			if !hasSuffixFold(mx.Host, tt.host) {
 				t.Errorf("got %v; want a record containing %s", mx, tt.host)
 			}
 		}
@@ -193,9 +197,7 @@ func TestLookupGmailNS(t *testing.T) {
 			t.Error("got no record")
 		}
 		for _, ns := range nss {
-			// Some nameservers alter the case of NS records. See #34446.
-			host := strings.ToLower(ns.Host)
-			if !strings.HasSuffix(host, tt.host) {
+			if !hasSuffixFold(ns.Host, tt.host) {
 				t.Errorf("got %v; want a record containing %s", ns, tt.host)
 			}
 		}
@@ -281,7 +283,7 @@ func TestLookupGooglePublicDNSAddr(t *testing.T) {
 			t.Error("got no record")
 		}
 		for _, name := range names {
-			if !strings.HasSuffix(name, ".google.com.") && !strings.HasSuffix(name, ".google.") {
+			if !hasSuffixFold(name, ".google.com.") && !hasSuffixFold(name, ".google.") {
 				t.Errorf("got %q; want a record ending in .google.com. or .google.", name)
 			}
 		}
@@ -373,7 +375,7 @@ func TestLookupCNAME(t *testing.T) {
 			}
 			t.Fatal(err)
 		}
-		if !strings.HasSuffix(cname, tt.cname) {
+		if !hasSuffixFold(cname, tt.cname) {
 			t.Errorf("got %s; want a record containing %s", cname, tt.cname)
 		}
 	}
@@ -658,7 +660,7 @@ func testDots(t *testing.T, mode string) {
 		t.Errorf("LookupAddr(8.8.8.8): %v (mode=%v)", err, mode)
 	} else {
 		for _, name := range names {
-			if !strings.HasSuffix(name, ".google.com.") && !strings.HasSuffix(name, ".google.") {
+			if !hasSuffixFold(name, ".google.com.") && !hasSuffixFold(name, ".google.") {
 				t.Errorf("LookupAddr(8.8.8.8) = %v, want names ending in .google.com or .google with trailing dot (mode=%v)", names, mode)
 				break
 			}
@@ -679,7 +681,7 @@ func testDots(t *testing.T, mode string) {
 		t.Errorf("LookupMX(google.com): %v (mode=%v)", err, mode)
 	} else {
 		for _, mx := range mxs {
-			if !strings.HasSuffix(mx.Host, ".google.com.") {
+			if !hasSuffixFold(mx.Host, ".google.com.") {
 				t.Errorf("LookupMX(google.com) = %v, want names ending in .google.com. with trailing dot (mode=%v)", mxString(mxs), mode)
 				break
 			}
@@ -692,7 +694,7 @@ func testDots(t *testing.T, mode string) {
 		t.Errorf("LookupNS(google.com): %v (mode=%v)", err, mode)
 	} else {
 		for _, ns := range nss {
-			if !strings.HasSuffix(ns.Host, ".google.com.") {
+			if !hasSuffixFold(ns.Host, ".google.com.") {
 				t.Errorf("LookupNS(google.com) = %v, want names ending in .google.com. with trailing dot (mode=%v)", nsString(nss), mode)
 				break
 			}
@@ -704,11 +706,11 @@ func testDots(t *testing.T, mode string) {
 		testenv.SkipFlakyNet(t)
 		t.Errorf("LookupSRV(xmpp-server, tcp, google.com): %v (mode=%v)", err, mode)
 	} else {
-		if !strings.HasSuffix(cname, ".google.com.") {
+		if !hasSuffixFold(cname, ".google.com.") {
 			t.Errorf("LookupSRV(xmpp-server, tcp, google.com) returned cname=%v, want name ending in .google.com. with trailing dot (mode=%v)", cname, mode)
 		}
 		for _, srv := range srvs {
-			if !strings.HasSuffix(srv.Target, ".google.com.") {
+			if !hasSuffixFold(srv.Target, ".google.com.") {
 				t.Errorf("LookupSRV(xmpp-server, tcp, google.com) returned addrs=%v, want names ending in .google.com. with trailing dot (mode=%v)", srvString(srvs), mode)
 				break
 			}